I've messed with the open source stuff quite a bit. It is a nice concept I guess but currently the link you posted before (
http://www.thesentryproject.com ) is just worlds better the any of that other stuff. Well, it depends on what you're after. If you just want to spend hours and hours tinkering but don't really care about how good the end result is then go with one of the small open source projects. However, if you need it to work correctly and well in real life scenarios then the only choice is
http://www.thesentryproject.com (IMO). As far as cost goes, I ended up wasting more money and time fussing with arduinos, compilers, and junk before I finally just bought the $50 kit from the sentry project. Doing the math, if I had just gone with them in the first place it would've cost me a lot less for much better result. Lessons learned I guess...